1. Field of the Application
The present invention relates to cases for electric devices. The invention has particular application to monitors for electric fields, such as voltage detectors, specifically the low-frequency fields of the type which surround high-voltage conductors, such as power transmission and distribution lines.
2. Description of the Related Art
Transmission lines route high-voltage (e.g., 2000 volts and higher) electrical power from power plants to main regional stations and local substations. Distribution lines route high-voltage electrical power from substations to end users. Many such lines require frequent inspection, repair, and/or maintenance. Contact with such high-voltage power lines can be fatal for workers. Monitors and detectors exist that can sense the proximity to dangerous high-voltage power lines and that can warn workers before they reach a dangerous proximity. One such type of detector senses an electric field surrounding a high-voltage conductor, the strength and extent of such a field being proportional to the voltage level. Such detectors typically provide an audible and/or visible indication of the detected field to warn the user.
Some detectors of the personal or wearable type can be battery-powered and have on/off switches. One difficulty, particularly with detectors having audible alarm signals, is that when a worker has to work for an extended period of time in a sensed electric field, the continuous audible alarm can become annoying. Thus, workers will frequently turn off the detector, which can be dangerous. Also, a worker must remember to turn the device on each time he or she wears it, and failure to remember this is also dangerous. Other devices, which can also be battery operated, can be designed to be always on. By being always on, the device can always be checking for the presence of high voltage electric fields and can always be working to provide for the safety of its users.
U.S. Pat. No. 6,329,924 and U.S. Design Pat. No. D439,537, the disclosures of which are hereby incorporated by reference in their entirety, disclose and depict wearable electric field detectors.